Black holes :: essays research papers

black hole,in astronomy, celestial object of such(prenominal) extremely intense gravity that it attracts everything near it and in some instances pr takingss everything, including light, from escaping. The term was first used in reference to a dealer in the last phases of gravitational collapse (the last-place stage in the life history of certain lead storys see stellar evolution), by the American physicist John A. Wheeler. Gravitational collapse begins when a star has depleted its steady sources of thermonuclear energy and can no longer produce the expansive force, a result of normal gas pressure, that supports the star against the compressive force of its own gravitation. As the star shrinks in coat (and increases in density), it may assume one of several forms depending upon its mass. A less massive star may become a whiteness dwarf, while a more massive one would become a supernova. If the mass is less than three times that of the sun, it will form a neutron star. However, if the final mass of the remaining stellar core is more than three solar masses, as shown by the American physicists J. Robert Oppenheimer and Hartland S. Snyder in 1939, nothing remains to prevent the star from collapsing without limit to an indefinitely small size and infinitely large density, a point called the "singularity.At the point of singularity the effects of Einsteins general theory of theory of relativity become paramount. According to this theory, space becomes curved in the vicinity of matter the greater the concentration of matter, the greater the curvature. When the star (or supernova remnant) shrinks below a certain size determined by its mass, the extreme curvature of space seals off contact with the outside world. The place beyond which no radiation can escape is called the event horizon, and its radius is called the Schwarzschild radius after the German astronomer Karl Schwarzschild, who in 1916 postulated the existence of collapsed celestial objects that em it no radiation. For a star with a mass bear on to that of the sun, this limit is a radius of only 0.9 mi (1.5 km). Even light cannot escape the black hole but is turned back by the vast pull of gravitation.It is now believed that the origin of some black holes is nonstellar. Some astrophysicists suggest that immense volumes of interstellar matter can collect and collapse into supermassive black holes, such as are found at the center of some galaxies.